In one known form of power transmission drive, the drive is intended for connection to a reciprocating engine as the prime mover. In testing such drives, however, the prime mover is conventionally an electric motor which permits such testing with improved safety, reduced noise and improved adjustability and control of the operating characteristics.
A problem arises, however, in the testing of drive systems by substitution of the relatively constant speed electric motor for the reciprocating engine in that the stresses loaded on the drive are not the same because of the lack of the periodic variation in the drive forces and speed.
One attempted solution to this vexatious problem has been the use of a universal joint connected between the electric motor and input shaft of the drive. The universal joint is connected at an angle so as to provide a variable output speed which varies, to some extent, similarly to that of the reciprocating engine.
Such prior testing apparatuses have further included means for adjusting the angularity of the universal joint so as to adjust the speed variations produced by the system in testing the power transmission drive.
Another problem found in the testing apparatus of the prior art is caused by the characteristics of the drive, which itself may have reciprocating components so as to provide periodically variable load characteristics. Illustratively, the load torque may vary as to pressure angle as a result of the rotation of a cam, or as a result of variable compression and exhaust, such as in a gas compressor.